NEW YORK — A key informant at the heart of the largest insider-trading case in U.S. history has asked a federal judge for lenient sentencing on her own crimes, explaining that soaring monthly bills and crumbling finances pressured her into a return to lawbreaking.

Roomy Khan, a former Intel executive who went from Wall Street success to vilified federal prosecution source, wrote in a newly filed sentencing letter that she engaged in insider trading from 2004-2007 because she faced roughly $72,000 in monthly housing and other expenses.

She also faced a threatened bank lawsuit, a separate legal case filed by her former housekeeper and a decimated investment portfolio, she wrote.

"I was getting desperate to make ends meet," Khan wrote in the letter to Manhattan U.S. District Court Judge Jed Rakoff, who is scheduled to sentence her on Thursday. "Slowly, the immorality and unlawfulness of insider trading was replaced by the desperate need to make money and pay my mounting bills. Also, the pervasiveness of this habit within most of the Wall Street professionals I came across made my decision/choices less dubious in my own mind."

Khan, who has a prior conviction for wire fraud, could face a maximum prison term of 20 years or more plus millions of dollars in fines based on her 2009 guilty plea to charges of insider trading, conspiracy and obstruction. But prosecutors are seeking leniency for the India-born informant, even though they noted in a Jan. 24 sentencing memorandum that she at times lied to investigators, tipped off suspected co-conspirators and destroyed evidence while she aided the government.

The prosecution memo cited Khan's major role in helping the government win the insider-trading conviction of former hedge fund billionaire Raj Rajaratnam by recording conversations in which the Galleon Group founder incriminated himself. He's now serving an 11-year prison term. Khan also testified against Douglas Whitman, a California hedge fund portfolio manager who was sentenced last week to two years in federal prison for his insider trading conviction.

The continuing federal probe has generated more than 70 arrests, convictions or guilty pleas to date.

In a separate defense sentencing memo, Khan attorney Stanislao German echoed prosecutors by citing his client's "extremely valuable" cooperation. Khan was deeply involved in aiding government cases that produced more than $250 million in fines, forfeitures and settlements, along with multiple convictions, German wrote.

He asked that Khan be sentenced to five years' probation, with no prison time. Media accounts have referred to her as a "rat," wrote German. In contrast with the government's victories, the India-born informant "has lost all of her money, her home, her friends and acquaintances, the value of her education, and has become an outcast within her own family," German wrote.

Ironically, Khan cited some of those same consequences as among the fears that led her to insider trading.

She said she was living in a costly Atherton, Calif., home with two mortgages.

"Over time, the shame and ignominy of losing my house and status in this society became more important than the unlawfulness of insider trading and the fear of getting caught," she wrote.

Khan reaped approximately $1,525,000 in profits by trading on illegal insider information in the stocks of Google, Polycom, Hilton hotels and Kronos, prosecutors wrote in their sentencing memorandum. Rajaratnam and others to whom she passed the illegal information collectively gained more than $25 million.

Confronted by the FBI in 2007, she began cooperating. But she wrote that her financial and personal situation continued a downslide.

She lost a job as a consultant with Trivium Capital Management, a hedge fund investment adviser. She was sued for alleged back wages by a former housekeeper, a case which she fabricated a document to help her defense. Federal investigators discovered that she lied to them about suspected co-conspirators and destroyed evidence — actions Khan said she took to protect associates and a relative.

Finally, she suffered a serious leg injury when she was struck by a taxi that jumped a curb in 2011. The leg still hasn't healed properly, German wrote.

"Nothing can defend my decisions through that time," wrote Khan. "All I can say is that I was in the middle of this massive storm that completely destroyed my life."

Today, she and her family have started over in a town where "no one really knew us," she wrote, describing her new life in a rental home as days of cooking, cleaning and other household chores.

"I treat my life now as part of my dues," Khan concluded, adding she hopes to "gain my self-respect and dignity back."